The present invention relates to electrical smoking systems that heat a cigarette upon detection of a draw taken on the cigarette.
Previously known conventional lit cigarettes deliver flavor and aroma to the user as a result of combustion of tobacco. A mass of combustible material, primarily tobacco, is oxidized as the result of applied heat with typical combustion temperatures in a conventional cigarette being in excess of 800xc2x0 C during puffing. Heat is drawn through an adjacent mass of tobacco by drawing on the mouth end of the cigarette. During this heating, inefficient oxidization of the combustible material takes place and yields various distillation and pyrolysis products. As these products are drawn through the body of the smoking device toward the mouth of the smoker, they cool and condense to form the aerosol which gives the consumer the flavor and aroma associated with smoking. Conventional lit cigarettes can produce side stream smoke during smoldering between puffs, which may be objectionable to some non-smokers. Also, once lit, conventional cigarettes must be fully consumed or be discarded.
Commonly assigned U.S. Pat. No. 5,388,594, which is incorporated herein by reference, discloses an electrical smoking system that includes novel electrically powered lighters and novel cigarettes that are adapted to cooperate with the lighters. The lighter includes a plurality of metallic heaters disposed in a configuration that slidingly receives a tobacco rod portion of the cigarette. One of the many advantages of such a smoking system is the reusability of the lighter for numerous cigarettes. One of the primary goals in an electrical smoking system such as that disclosed in U.S. Pat. No. 5,388,594, is to provide sensations of smoking that are as close as possible to the sensations experienced when smoking a conventional cigarette. Some of these sensations include the resistance-to-draw (RTD) experienced by a smoker taking a puff on the cigarette, and the length of time between when a smoker begins to draw on the cigarette and when the smoker can first detect the flavors and aromas associated with smoking the cigarette.
RTD of traditional cigarettes is the pressure required to force air through the full length of a standard cigarette at the rate of 17.5 ml per second. RTD is usually expressed in inches or millimeters of water. Smokers have certain expectations when drawing upon a traditional cigarette in that too little RTD or too much can detract from smoking enjoyment. More traditional cigarettes of moderate delivery have RTD""s generally within the range of approximately 100 to 130 mm""s water.
Establishing a desired RTD in electrical smoking systems is complicated by the circumstance that in smoking systems such as shown in U.S. Pat. Nos. 5,388,594 and 5,692,525, air is first drawn through passages within the cigarette lighter before being drawn out through the cigarette. The filter tipping of the cigarettes of those systems are preferably flow-through and/or low particulate efficiency filters so as to minimize loss of whatever smoke is produced. Such filters produce little pressure drop and therefore do not contribute much RTD. Consequently, prior practices have included the establishment of RTD (or pressure drop) predominantly in the lighter portion of the electrical smoking system, such as with an annular frit (porous body) adjacent the air admission port of the lighter as taught in commonly assigned U.S. Pat. No. 5,954,979, incorporated herein by reference. Because pressure drop varies widely with any change in size of the constriction, it has been found that the frits or other forms of tiny flow constrictions in the lighter body must be manufactured with care. It therefore adds expense and other production and quality concerns. Furthermore, tiny flow passages are prone to clog, particularly in lighters wherein any smoke is allowed to linger after completion of a puff.
Further, establishing a quick response time for electrically heating a portion of the cigarette with one or more heater elements in response to a puff is a desirable characteristic. To achieve an equivalent experience to traditional cigarette smoking, ideally the heating of the cigarette would be instantaneous with the beginning of a puff cycle. However, sensing systems typically have some delay time between the beginning of a puff cycle and the heating of the cigarette with one or more heaters.
The heating fixture in an electrical smoking system such as that shown in commonly assigned U.S. Pat. Nos. 5,388,594 and 5,878,752, which are herein incorporated in their entireties by reference, includes a plurality of radially-spaced heating blades supported to extend from a hub and that are individually energized by a power source under the control of electrical circuitry to heat a number of discrete heating zones around the periphery of an inserted cigarette. Eight heating blades are preferred to develop eight puffs as in a conventional cigarette, although a greater or lesser number of heating blades can be provided.
The electrical circuitry in electrical smoking systems can be energized by a puff sensitive sensor that is sensitive to pressure drops occurring when a smoker draws on the cigarette. The puff sensor activates an appropriate one of the cigarette heater elements or blades as a result of a change in pressure when a smoker draws on the cigarette. A sensor that relies on detection of a pressure drop in order to initiate the smoking event may require a RTD through the cigarette that a smoker finds to be higher than the RTD with a conventional cigarette. The electrical smoking system should preferably provide a RTD that is as close to a conventional cigarette as possible, while also avoiding false signals and undesired actuation of the heater blades that may occur as a result of shock vibration or air flow through the system created by factors other than a smoker drawing on the cigarette, such as movement of the cigarette smoking system or air movement past the cigarette smoking system.
An embodiment of an electrically heated cigarette smoking device in accordance with the invention includes a heater unit, a plurality of heaters within the heater unit for applying heat to portions of a cigarette supported within the heater unit, the heater unit having an opening adapted to receive an end of a cigarette and adapted to position the end in proximity to the plurality of heaters, and the heater unit defining at least part of a suction flow passage through which ambient air is drawn into contact with the cigarette when a smoker draws on the cigarette positioned in the heater unit. A housing is mated with the heater unit and is designed to be comfortably grasped by a smoker. A partition positions the heater unit relative to the housing and at least partially defines a bypass flow passage in fluid communication with ambient air surrounding the housing, the partition further defining a flow diverting passage through which ambient air is drawn from the bypass flow passage into the suction flow passage when a smoker puffs on a cigarette inserted in the heater unit opening. A sensor can be positioned in the flow diverting passage or in the suction flow passage, and preferably in the flow diverting passage leading to the suction flow passage, to provide a signal indicative of a smoker taking a puff on the cigarette.
In an alternative embodiment, the housing of the electrically heated cigarette smoking device can include a chamber that is formed around at least part of the filter end of the cigarette when the cigarette is inserted into the housing. A vacuum or pressure drop sensor can be ported to the chamber and will consequently sense the vacuum or pressure drop created at this location. Openings in the cigarette at this location allow for the sensing of internal vacuum created within the cigarette when a smoker takes a puff on the cigarette. This arrangement can provide a faster response time than an arrangement wherein RTD (or pressure drop) is established predominantly in the lighter portion of the electrical smoking system, such as with an annular frit (porous body) adjacent the air admission port of the lighter as taught in commonly assigned U.S. Pat. No. 5,954,979.